The present invention relates to a two-stage locking push switch which is provided with an actuator having two locking positions, and more particularly to a two-stage locking push switch of the type in which when the actuator is depressed by one step into the switch casing, it is locked at a first position where it places the switch in its first state, and when the actuator is further depressed by another step it is locked at a second position where it places the switch in its second state, and when the actuator is further depressed by another step it is returned to its initial position where it holds the switch in its initial state (usually in the OFF state).
This kind of two-stage locking push switch is employed, for example, as an actuating switch of an automotive air conditioner. When the actuator is depressed by one step from the inoperative state of the air conditioner and is locked at a first position, the air conditioner is placed in its normal operative state in which its cooling power is relatively large and the inside of the car is cooled properly. When the actuator is further depressed by another step and locked at a second position, the air conditioner is put in its economical running state in which its cooling power is lowered to reduce power consumption. Then, when further depressed by another step, the actuator springs back to its initial position where the air conditioner is out of operation.
For displaying the individual operative states of the switch, the prior art has utilized such an arrangement as follows: a forwardly extending optical path of the switch casing on the side of the actuator (usually in the form of a push button) is divided into two optical paths, in which two lamps are respectively disposed. When the actuator is at the abovesaid first position, the two lamps are both lighted to illuminate the entire area of the front of the actuator (the top end face of the push button). When the actuator is at the abovesaid second position, only one of the lamps is lighted to illuminate the half of the entire area of the front of the actuator.
As mentioned above, the conventional two-stage locking push switch employs two lamps and sometimes lights them at the same time, in which case they give off much heat, raising the temperature of the switch and resulting in the service life of the lamps being short. Furthermore, the switch must be constructed so that it withstands high temperatures and the lamps are relatively expensive, increasing the manufacturing cost of the switch.
Moreover, the conventional push switch of this kind is designed so that when the actuator is pushed by a stroke past the first locking position and down to the second locking position, an operator can feel it immediately by the touch on the actuator. But such a structure introduces the possibility that once depressed to an extremity of a stroke, the actuator may not be locked at either of the first and second positions but may be returned to its initial position. Furthermore, the situation occasionally arises where although the actuator is locked at the second position when depressed from its initial position, the touch is so soft that it is difficult to judge whether the actuator is locked at the first or second position.
Such a conventional two-stage locking push switch is disclosed, for example, in U.S. Pat. No. 4,467,159 (issued on Aug. 21, 1984). Prior art problems will be described with reference to FIGS. 1 and 2, which show a slight modification of this United States patent to resemble the present invention in arrangement of a hook spring.
A moving member 12 is slidably mounted in an elongated tubular casing 11 having a rectangular crosssection. An actuator (a push button) 13 is mounted on that portion of the moving member 12 projecting out from the tubular casing 11. A coiled spring 14 is interposed between the moving member 12 and the rear panel of the tubular casing 11, by which the moving member 12 is biased forwardly, that is, in such a direction that the actuator 13 projects out of the tubular casing 11. A hook spring 15 is provided to extend above the moving member 12 in the front-to-back direction of the casing 11. The rear end of the hook spring 15 is secured as by winding in a coil form to an auxiliary plate 16 fixed to the rear panel of the tubular casing 11. The free end of the hook spring 15 is bent substantially at right angles towards the moving member 12 to form an engaging portion 18 for resilient engagement with the moving member 12. As the moving member 12 moves in the axial direction, the engaging portion 18 slides on a sliding face 17 of the moving member 12. The sliding face 17 has protrusively provided thereon first and second heart cams 21 and 22. The heart cams 21 and 22 are disposed with their recessed portions 23 and 24 facing the actuator 13, and they are staggered relative to each other both in the axial direction and in the direction perpendicular thereto. The sliding face 17 has a raised portion 26 along the first and second heart cams 21 and 22 on one side thereof and the engaging portion 18 of the hook spring 15 is urged towards the raised portion 26, that is, to the left in FIGS. 1 and 2. The sliding face 17 has another raised portion 27 on the side of the actuator 13. A projection 27a is provided which projects from the raised portion 27 towards the recessed portion 24 of the second heart cam 22.
Adjacent the sliding face 17 is provided a high land 63 on which movable contact pieces 31 and 32 are mounted. The high land 63 is higher than the first and second heart cams 21 and 22. A guide bank 28 is provided which extends from the vicinity of the recessed portion 23 of the first heart cam 21 and along the second heart cam 22 on the side of the contact pieces 31 and 32. A blocking projection 29 is provided which extends from the axially central portion of the guide bank 28 to the high land 63.
FIG. 2 illustrates on an enlarged scale the sliding face 17 which has formed thereon the heart cams 21, 22 shown in FIG. 1. A first displacement passing l.sub.1 of the engaging portion 18 of the hook spring 15 is formed from a starting point P.sub.1 (where the actuator 13 is at the most protruded position) to the recessed portion 23, as indicated by the broken line. That is, when the actuator 13 is depressed into the casing 11, the engaging portion 18 starts to slide on the sliding face 17 at the point P.sub.1, displaces along the side face of the first heart cam 21 and then strikes against the blocking projection 29 to slide into the recessed portion 23. From the recessed portion 23 to the recessed portion 24 there is formed a second displacement passage l.sub.2 along the side face of the second heart cam 22, as indicated by the one-dot chain line. From the recessed portion 24 of the second heart cam 22 to the starting point P.sub.1 of the first displacement passage l.sub.1 there is formed a third displacement passage l.sub.3 , as indicated by the two-dot chain line. Between the end of the passage l.sub.3 and the beginning of the passage l.sub.1 there is formed a step in alignment with the passage l.sub.1,as indicated by the line 82, so that the sliding face 17 is lower on the side of the passage l.sub.1 than on the side of the passage l.sub.3.
When the actuator 13 is depressed by one step from its most protruded position into the switch casing 11, the engaging portion 18 of the hook spring 15 displaces on the sliding face 17 along the first passage l.sub.1 and then strikes against the blocking projection 29. Feeling the strike, an operator releases his hand from the actuator 13, allowing the engaging portion 18 to displace, by its own biasing force, towards the guide bank 28. At the same time, the actuator 13 is urged by the coiled spring 14 (FIG. 1) to project out of the casing 11, so that the engaging portion 18 is moved into the recessed portion 23. That is, the hook spring 15 is caught on the heart cam 21 and the moving member 12 is locked at this first position relative to the tubular casing 11.
When the actuator 13 is further depressed by another step into the casing 11 from the first position, the engaging portion 18 displaces along the recessed portion 23 towards the second heart cam 22 and then displaces along the side face of the second heart cam 22, that is, the engaging portion 18 moves along the second passage l.sub.2 and strikes against the raised portion 27. Again feeling the strike, the operator releases his hand from the actuator 13, allowing the engaging portion 18 to be forced into the recessed portion 24 by the biasing force of the hook spring 15 and the returning force of the actuator 13. Thus the hook spring is caught on the heart cam 22 and the moving member 12 is locked at this second position.
When the operator releases his hand from the actuator 13 after further depressing it from the second position, the moving member 12 is moved back by the coiled spring 14, by which the engaging portion 18 returns to its starting point P.sub.1 via the third displacement passage l.sub.3.
As described above, in the conventional two-stage push switch, the moving member is locked at the first position releasing the actuator in response to the striking of the engaging portion 18 against the blocking projecting 29 in the first actuator depressing operation. If, however, the actuator is depressed too forcibly, the hook spring 15 is likely to be deformed or broken. To avoid this, the prior art push switch is arranged so that when the actuator is depressed too forcibly, the engaging portion 18 gets over the blocking projection 29. In such a case, the engaging portion 18 follows the broken-line passage l.sub.4 to move along the guide back 28 on the side opposite from the second heart cam 22 to reach the side face of the projection 27a. When releasing the actuator 13, the engaging portion 18 settles into the recessed portion 24.
In practice, however, there are cases where when dashing against the blocking projection 29, the engaging portion 18 jumps up onto the guide bank 28 owing to the lateral biasing force of the hook spring 15 and thence moves across the second heart cam 22 along the broken-line passage l.sub.5 to reach the corner portion between the raised portions 26 and 27 and thence returns to the starting point via the passage l.sub.3 upon release of the actuator 13. That is, the moving member 12 is not locked at either of the first and second positions relative to the casing 11.
When the height of the blocking projection 29 is reduced so as to avoid such a situation, it is difficult to discern when the engaging portion strikes against the blocking projection 29, whereas when its height is too large, it is likely to bend the hook spring 15. Accordingly, it is necessary to set the shape and height of the blocking projection 29 at optimum values in accordance with the force of the hook spring 15, the shape of the engaging portion 18, the shape of the first passage l.sub.1, the height and shape of the guide bank 28, the biasing force of the coiled spring 14, etc. but this is difficult to achieve.